Arabic mathematician and physicist known to the West largely for his work in geometry under the name Alhazen. The most famous problem he solved dealt with locating the point on a surface from which light at a point of origin will be reflected to another specific point. He wrote about difficulties in the standard text of geometry inherited from the Greeks and applied geometrical methods to analyzing problems in optics. His work on the area of crescent-shaped figures (lunes) went beyond what was available in Greek texts.